A typical ink-jet printer includes one or more cartridges that contain a reservoir of ink. The reservoir is connected to a printhead that is mounted to the body of the cartridge.
The printhead is controlled for ejecting minute droplets of ink from the printhead to a printing medium, such as paper, that is advanced through the printer. The ejection of the droplets is controlled so that the droplets form images on the paper.
The printhead includes a substrate, which is a conventional silicon wafer upon which has been grown a dielectric layer, such as silicon dioxide. The ink droplets are ejected from small ink chambers carried on the substrate. The chambers (designated "firing chambers") are formed in a component known as a barrier layer. The barrier layer is made from photosensitive material that is laminated onto the printhead substrate and then exposed, developed, and cured in a configuration that defines the firing chambers.
The primary mechanism for ejecting a droplet is a heat transducer, such as a thin-film resistor. The resistor is carried on the printhead substrate. The resistor is covered with suitable passivation and other layers, as is known in the prior art, and connected to conductive layers that transmit current pulses for heating the resistors. One resistor is located in each of the firing chambers.
In a typical printhead, the ink droplets are ejected through orifices that are formed in an orifice plate that covers most of the printhead. The orifice plate may be electroformed with nickel and coated with a precious metal for corrosion resistance. Alternatively, the orifice plate is made from a laser-ablated polyimide material. The orifice plate is bonded to the barrier layer and aligned so that each firing chamber is continuous with one of the orifices.
The firing chambers are refilled with ink after each droplet is ejected. In this regard, each chamber is continuous with an ink channel that is formed in the barrier layer. The channels extend toward an elongated ink feed slot that is formed through the substrate. The ink feed slot may be located in the center of the printhead with firing chambers located on opposite long sides of the feed slot. The slot is made after the ink-ejecting components (except for the orifice plate) are formed on the substrate.
The just mentioned components (barrier layer, resistors, etc) for ejecting the ink drops are mounted to the front side of the printhead substrate. The back side of the printhead is mounted to the body of the ink cartridge so that the ink slot is in fluid communication with an opening to the reservoir. Thus, refill ink flows through the ink feed slot from the back side of the substrate toward the front of the substrate and then across the front side through the channels (and beneath the orifice plate) to refill the chambers.
One prior method of forming the ink feed slot in the substrate involved abrasive jet machining as described in U.S. Pat. No. 5,105,588, hereby incorporated by reference. This prior approach uses compressed air to force a stream of very fine particles (such as aluminum oxide grit) to impinge on the substrate for a time sufficient for the slot to be formed. This abrasive jet machining is often referred to as drilling or sandblasting. In prior the art, the nozzle from which the particles are emitted is spaced a short distance from the back of the substrate during the entire drilling process.
The portion of the front side of the substrate between the slot and the ink channels is known as the printhead "shelf." Preferably this shelf length is designed to be as short as possible because as the length of the shelf increases (i.e., the distance the ink must flow from the slot to enter the ink channels) there is an attendant decrease in the frequency with which ink droplets may be ejected from the firing chambers.
The edge defined by the junction of the slot and the shelf is designated as the shelf edge. Prior approaches to forming the ink feed slot by abrasive jet machining as described above produced uneven shelf edges. Thus, the length of the shelf had to be designed with significant tolerances to account for the uneven shelf edge.
The present invention is directed to a technique for controlling the abrasive jet machining process to drill an ink feed slot that results in a relatively even shelf edge. The evenness of the shelf edge reduces the tolerances required for designing the shelf length, thus permitting the construction of printheads with minimized shelf lengths and a correspondingly increased droplet ejection frequency. The printhead size is correspondingly reduced.
As another aspect of this invention, the characteristic taper in the width of the slot (that is, the drilled slot widens from the front side to the back side of the substrate as a result of the abrasive-jet machining process) is dramatically reduced. These reduced-taper ink feed slots are particularly advantageous in printhead designs with multiple feed slots since more slots may be accommodated on a given size substrate than is possible with slots using the prior approach.
Other advantages and features of the present invention will become clear upon study of the following portion of this specification and the drawings.